Implants and infection
With the increasing use of medical implants, we are also increasingly confronted with infectious biofilms on them. The most common implants include joint prostheses, osteosyntheses, vascular prostheses, pacemakers and defibrillators, dental implants, neurosurgical shunts and breast implants.
The therapeutic success of implant infections depends on a precise microbiological diagnosis. Because microorganisms form biofilms on foreign bodies, they are often difficult to detect in surrounding tissue. Biofilms consist of an amorphous matrix of polymerized polysaccharide in which microorganisms are embedded. In the biofilm, microorganisms are in a metabolically inactive, stationary growth phase. Over weeks to years, a complex three-dimensional layer develops which ensures the nutrition of the biofilm (via water channels) and its communication (via extracellular messenger substances) via rudimentary structures.
While free living (planktonic) bacteria are killed by antibiotics and the immune system, adherent bacteria survive protected in the extra cellular matrix of the biofilm.
Technical details can be found in the data sheet.
Significance and principle of action of sonication
Through sonication (ultrasound), microorganisms can be gently removed from the surface of an infected implant. The implant is immersed in liquid so that the ultrasound waves can act on the entire implant surface. After sonication, the liquid (the sonicat) is prepared for cultures and can then immediately be used for subsequent analysis (e.g. PCR). Sonication enables rapid diagnosis of the site of infection if implants have to be removed.
Detection of biofilm-forming bacteria
The implant is aseptically removed from the body in the operating room and transported to the microbiology laboratory in a sterile box within 24 hours. After addition of Ringer’s solution, the implant is shaken vigorously and exposed to ultrasound for 1 minute.
The sonication removes > 99.9% of the adherent bacteria.
Quantitative detection of biofilm-forming bacteria
The sonication is microbiologically processed and the amount of bacteria is quantified (number of colony forming units per ml sonication fluid). Sonication can detect up to 10,000 times more bacteria than conventional methods, such as biopsies of periprosthetic tissue. This allows better detection of mixed infections and different bacterial morphotypes.
The sensitivity is particularly improved in patients with previous antibiotic therapy because the bacteria protected in the biofilm survive better.
In order to gently remove the biofilm, the implant, which is deposited in a box with liquid, is placed in the BactoSonic® specially developed for this procedure; a sonication in an ordinary ultrasound bath would kill the microorganisms. Low-frequency ultrasound with low intensity in the area of the cavitation threshold is used. The adhesion of the biofilm to the implant surface is reduced by microcurrents, shear forces and oscillating cavitation bubbles to such an extent that it detaches from the implant during the ultrasonic treatment. Any cavitation events that occur are still so low in energy that no significant destruction of cell structures occurs. The microorganisms obtained in the sonication can be cultivated directly or detected promptly by other methods.
Planktonic and biofilm forms of bacteria
Biofilm on the implant surface
Success of biofilm removal
Comparison of cultures of tissue biopsy and sonication fluid (Sonikat)
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17. Trampuz A., Piper KE, Jacobson MJ, Hanssen AD, Unni KK, Osmon DR, Mandrekar JN, Cockerill FR, Steckelberg JM, Greenleaf JF, Patel R. Sonication of removed hip and knee prostheses for diagnosis of infection. N Engl J Med 2007; 357: 654-63.www.ncbi.nlm.nih.gov/pubmed/17699815
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